Printed circuit board and manufacturing method thereof

ABSTRACT

A printed circuit board is disclosed. A printed circuit board, which includes a first board part, a flexible board part which has one side coupled with the first board part and which includes an electrical wiring layer and an optical waveguide to transmit both electrical signals and optical signals, and a second board part coupled with the other side of the flexible board part, where the electrical wiring layer and the optical waveguide are disposed with a gap in-between, can provide greater bendability and reliability, by having the optical waveguide and electrical wiring layer separated with a gap in-between at the flexible portion of the board, and the optical waveguide can be manufactured with greater precision for even higher reliability, by having the optical waveguide manufactured separately and then inserted during the manufacturing process of the board.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. divisional application filed under 35 USC1.53(b) claiming benefit of U.S. Ser. No. 11/984,114 filed in the UnitedStates on Nov. 13, 2007, which claims earlier benefit to Korean PatentApplication No. 10-2006-0115391 filed with the Korean IntellectualProperty Office on Nov. 21, 2006, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board.

2. Description of the Related Art

A rigid-flexible printed circuit board is in wide use in networkequipment and mobile electronic products such as cell phones, etc. Inmobile electronic products, in particular, there is a high demand forprinted circuit boards having flexibility, since maneuverability isrequired of folders, sliders, or more complicated structures.

Compared to boards using electrical copper wiring, boards that useoptical signals are unaffected by EMI and EMC, so that they may be moreresistant to external noise and may not require the use of grounds ordifferential wiring. There may also be the advantage of enabling thetransfer of high-speed signals, due to low loss.

An example of a conventional structure for embedding an opticalwaveguide in a flexible or rigid-flexible printed circuit board is asillustrated in FIG. 1A and FIG. 1B. Since it is effective to use copperwiring, even in a printed circuit board having an embedded opticalwaveguide, for transferring electrical power and low-speed analogsignals, a board structure is generally presented in which electricalwiring and optical wiring are included together.

With the flexible or rigid-flexible printed circuit board, it may berequired to provide sufficient bendability and high reliability in thebending portions. The bending characteristics may be determined by thethickness and strength of the flexible portions and the stiffness andstrength of the material, while it may be especially desirable to keepthe thickness small.

However, in the structure of a conventional printed circuit board havingan embedded optical waveguide, the electrical wiring layer and theoptical waveguide layer are attached, so that there is less bendabilitycompared to typical electrical wiring boards, and there is a higher riskof defect or reliability problems.

SUMMARY OF THE INVENTION

An aspect of the invention is to provide a printed circuit board and amethod of manufacturing a printed circuit board, which offer greaterbendability and reliability, by having the optical waveguide andelectrical wiring layer separated with a gap in-between at the flexibleportion of the board.

One aspect of the claimed invention may provide a printed circuit board,which includes a first board part, a flexible board part which has oneside coupled with the first board part and which includes an electricalwiring layer and an optical waveguide to transmit both electricalsignals and optical signals, and a second board part coupled with theother side of the flexible board part, where the electrical wiring layerand the optical waveguide are disposed with a gap in-between.

A groove may be formed in the first board part to install the opticalwaveguide. The groove may be adjacent to the optical waveguide and maybe exposed to the exterior. A pad may be formed on a predeterminedposition of the optical waveguide adjacent to the groove, to mount theoptical waveguide on. Here, the pad may be formed on the surface of theoptical waveguide or may be buried in the optical waveguide.

Also, a rewiring land may be formed on the optical waveguide that iselectrically connected with the pad, where the rewiring land, similar tothe pad, may be formed on the surface of the optical waveguide or may beburied in the optical waveguide.

A via may be formed on the first board part for interlayer connection,where the rewiring land may be electrically connected with the via.

Another aspect of the claimed invention may provide a printed circuitboard, which a first board, on a side of which a first ledge is formed,a second board, on a side of which a second ledge is formed and which isdisposed with a gap of a predetermined distance with respect to thefirst board, a flexible optical waveguide having either end mounted oneach of the first ledge and the second ledge, and a first outer boardand a second outer board stacked respectively on the first board and thesecond board such that either end of the flexible optical waveguide arecovered.

A groove may be formed in the first outer board to install the opticalwaveguide. The groove may be adjacent to the optical waveguide and maybe exposed to the exterior. A pad may be formed on a predeterminedposition of the optical waveguide adjacent to the groove, to mount theoptical waveguide on. Here, the pad may be formed on the surface of theoptical waveguide or may be buried in the optical waveguide.

Also, a rewiring land may be formed on the optical waveguide that iselectrically connected with the pad, where the rewiring land, similar tothe pad, may be formed on the surface of the optical waveguide or may beburied in the optical waveguide.

A via may be formed on the first board part for interlayer connection,where the rewiring land may be electrically connected with the via.

Yet another aspect of the claimed invention may provide a method ofmanufacturing a printed circuit board having a flexible opticalwaveguide to transmit optical signals, which includes preparing a firstboard and a second board that are disposed with a gap in-between,forming a ledge on each of the first board and the second board suchthat either end of the flexible optical waveguide is mounted on each ofthe ledges, stacking the flexible optical waveguide on the first boardand the second board such that the flexible optical waveguide is mountedby way of the ledges, and stacking a first outer board and a secondouter board respectively on the first board and the second board suchthat either end of the flexible optical waveguide is covered.

A groove may be formed adjacent to the flexible optical waveguide in thefirst outer board, the groove configured to have the optical waveguideinstalled therein.

A groove may be formed adjacent to the flexible optical waveguide in thefirst outer board to install the optical waveguide, a pad may be formedon a predetermined position of the optical waveguide adjacent to thegroove to mount the optical waveguide.

The flexible optical waveguide may include a core, through which opticalsignals propagate, and a cladding, which covers the core. Here, the padmay be formed by forming a conductive pattern on a carrier whichcorresponds to the pad, and pressing the cladding and the carrier suchthat the conductive pattern is transcribed onto the cladding.

Also, an additional rewiring land may be formed on the flexible opticalwaveguide that is electrically connected with the pad, where therewiring land may be formed by forming a conductive pattern on a carrierthat corresponds to the rewiring land, and pressing the cladding and thecarrier such that the conductive pattern is transcribed onto thecladding.

Additional aspects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are cross-sectional views illustrating a printedcircuit board according to prior art.

FIG. 2 is a cross-sectional view illustrating a printed circuit boardaccording to a first disclosed embodiment of the invention.

FIG. 3 is a cross-sectional view illustrating a printed circuit boardaccording to a second disclosed embodiment of the invention.

FIG. 4 is a cross-sectional view illustrating a printed circuit boardaccording to a third disclosed embodiment of the invention.

FIG. 5 is a cross-sectional view illustrating a printed circuit boardaccording to a fourth disclosed embodiment of the invention.

FIG. 6A and FIG. 6B are plan views illustrating portions on whichphotoelectric conversion elements are to be installed.

FIG. 7A and FIG. 7B are cross-sectional views illustrating portions onwhich photoelectric conversion elements are to be installed.

FIG. 8 is a flowchart illustrating a method of manufacturing a printedcircuit board according to another embodiment of the invention.

FIG. 9A, FIG. 9B, FIG. 9C and FIG. 9D are flow diagrams illustrating themethod of manufacturing a printed circuit board shown in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described below in more detail withreference to the accompanying drawings. In the description withreference to the accompanying drawings, those components are renderedthe same reference number that are the same or are in correspondenceregardless of the figure number, and redundant explanations are omitted.

First, the printed circuit board according to an aspect of the claimedinvention will be described.

FIG. 2 is a cross-sectional view illustrating a printed circuit boardaccording to a first disclosed embodiment of the invention. In FIG. 2are a illustrated first board part 110, a second board part 120, grooves112, 122, photoelectric conversion elements 114, 124, vias 116, 126,ledges 118, 128, a flexible board part 130, an optical waveguide 132, acore 132 a, a cladding 132 b, an electrical wiring layer 134, pads 136,patterns 137, and rewiring lands 138.

At either end of a printed circuit based on this embodiment may bepositioned the first board part 110 and the second board part 120, withthe flexible board part 130 positioned between the first board part 110and second board part 120 which has flexibility. That is, the flexibleboard part 130 may have both ends coupled to boards that are rigid.Here, the flexible board part 130 may be composed of an opticalwaveguide 132 for transmitting optical signals and an electrical wiringlayer 134 for transmitting electrical signals.

Compared to the electrical wiring layer 134, which may use copper wiringfor transmitting electrical signals, the optical waveguide 132 may bemore resistant to external noise and may not require the use of groundsor differential wiring. The optical waveguide 132 may also allow thetransfer of high-speed signals, due to low loss. The optical waveguide132 may be composed of a core 132 a, which may serve as a path for thetransfer of optical signals, and a cladding 132 b, which may surroundthe core 132 a.

The core 132 a may be the path for the transfer of optical signals, andmay be surrounded by the cladding 132 b. The core 132 a may be made of apolymer material or an optical fiber material. In this embodiment,however, a core is presented that is made of a polymer material, whichhas superb flexibility and which may be more desirable in terms ofminiaturizing the connecting structures with respect to thephotoelectric conversion elements.

The cladding 132 b may surround the core 132 a and may allow anefficient transmission of optical signals. Similar to the core 132 a,the cladding 132 b may also be made of a polymer material. However, forefficient transfer of optical signals, the cladding 132 b may bedesigned to have a refractive index lower than that of the core 132 a.

While the electrical wiring layer 134 may be less favorable, compared tothe optical waveguide 132 described above, in transferring high-speedsignals, it may be favorable when supplying electrical power, nothigh-speed digital signals. Thus, it may be possible to omit theelectrical wiring layer 134 and form only the optical waveguide 132, infields requiring only the transmission of high-speed digital signals.However, since electrical power and analog signals may also betransmitted from the main board to the display board in general devicessuch as cell phones, the electrical wiring layer 134 may be formed aswell as the optical waveguide 132.

FIG. 2 is a cross-sectional view illustrating a printed circuit board100 according to a first disclosed embodiment of the invention, in whicha flexible board part 130 is presented that has both the opticalwaveguide 132 and the electrical wiring layer 134.

In the first board part 110 and second board part 120, there may begrooves 112, 122 formed, in which the photoelectric conversion elements114, 124 may be installed. By mounting the photoelectric conversionelements 114, 124 in these grooves 112, 122, the overall thickness of aprinted circuit board 100 based on this embodiment may be reduced.

The photoelectric conversion elements 114, 124 may serve to convertelectrical signals to optical signals or convert optical signals toelectrical signals. The longer the distance from the photoelectricconversion elements 114, 124 to the optical waveguide 132, the greaterthe risk of errors created by losses and crosstalk in the opticalsignals. Thus, it may be advantageous to make the distance as short aspossible from the photoelectric conversion elements 114, 124 to theoptical waveguide 132.

To this end, in this embodiment, grooves 112, 122 may be formed in thefirst board part 110 and second board part 120, in which to install thephotoelectric conversion elements 114, 124. Because of these grooves112, 122, portions of the optical waveguide 132 may be exposed, and pads136 may be formed on portions of the optical waveguide thus exposed suchthat the photoelectric conversion elements 114, 124 may be mounted onthe pads 136.

Because of this structure, not only is the thickness reduced for theprinted circuit board 100 according to this embodiment, but also thereliability of the signals is increased.

With respect to thus forming the pads 136 on the optical waveguide 132,while the pads 136 may be formed on the surface of the optical waveguide132, the pads 136 may be buried in the optical waveguide 132, to furtherincrease the effects of reducing the overall thickness and increasingthe reliability of signals.

The pads 136 buried in the optical waveguide 132 may be formed by aprocess of first forming on a carrier (not shown) a conductive patterncorresponding to the pads, pressing the cladding 132 b and the carrier(not shown) together, and afterwards removing the carrier from thecladding 132 b, to transcribe the conductive pattern onto the cladding132 b.

In order that the circuit patterns (not shown) formed on the first boardpart 110 and second board part 120 and the photoelectric conversionelements 114, 124 may be electrically connected to each other, rewiringlands 138 may be formed on the optical waveguide 132 that areelectrically connected with the pads 136, and the rewiring lands 138 maybe electrically connected with the vias 116, 126 and circuit patterns(not shown) formed on the first board part 110 and second board part120.

Similar to the pads 136 described above, the rewiring lands 138 may beformed on the surface of the optical waveguide 132, but may also beburied in the optical waveguide 132, and may be formed by a methodsimilar to that used for the pads 136. That is, the rewiring lands 138may be formed by a process of first forming a conductive pattern on acarrier that is in correspondence with the rewiring lands, pressing thecladding and carrier together, and then removing the carrier from thecladding, to transcribe the conductive pattern onto the cladding.

As illustrated in FIG. 2, this embodiment presents a configuration inwhich the rewiring lands 138 are connected directly with the vias 116,126. Because the rewiring lands 138 are contacted through the vias 116,126, there may not be a need for considerations on either the platingcharacteristics with respect to the material forming the opticalwaveguide 132 or hole processing characteristics.

Also, in the case of the present embodiment, the pads 136 and therewiring lands 138, which are for contacting the photoelectricconversion elements 114, 124, may be positioned on the first board part110 and second board part 120, whereby the risk of loss of reliabilitydue to bending may be minimized.

That is, even though the pads 136 and the rewiring lands 138 forcontacting the photoelectric conversion elements 114, 124 may be formedon an optical waveguide 132 made of a flexible material, the first boardpart 110 and second board part 120 may be coupled at the upper and lowerparts around the portions of the optical waveguide 132 where the pads136 and the rewiring lands 138 are formed, to yield an effect similar tohaving the pads 136 and the rewiring lands 138 formed on an essentiallyrigid board, and thus ensure reliability.

In this embodiment, a structure is presented that has ledges 118, 128formed respectively on the first board part 110 and second board part120, and the optical waveguide 132 mounted on the ledges 118, 128. Thatis, both sides of the optical waveguide may each be covered by a rigidboard.

Due to this structure, there is less likelihood of detaching occurringbetween the layer on which the optical waveguide is formed and anadjacent layer, to provide superb reliability.

Furthermore, as a result of forming the ledges 118, 128 for mounting theoptical waveguide 132, portions of the layer on which the opticalwaveguide is formed may be the optical waveguide, while the remainingportions may be a rigid board. In this structure, the vias 116, 126 forinterlayer connection may be formed in the rigid board portions, and itmay not be necessary to form the vias in the optical waveguide, so thatthere may not be a need for considerations on either the platingcharacteristics with respect to the material forming the opticalwaveguide 132 or hole processing characteristics.

The electrical wiring layer 134 formed for transmitting electricalsignals may be implemented by forming circuit patterns (not shown) on aninsulation material high in flexibility, such as polyimide. As describedearlier, by disposing the electrical wiring layer 134 in separation fromthe optical waveguide 132, neither may be affected by the other'sbending, so that superb bendability and reliability may be provided.

FIG. 3 is a cross-sectional view illustrating a printed circuit board200 according to a second disclosed embodiment of the invention. In FIG.3 are illustrated a first board 210, a second board 220, vias 212, 222,ledges 218, 228, a flexible optical waveguide 230, pads 232, rewiringlands 234, a first outer board 240, a second outer board 250, grooves242, 252, and photoelectric conversion elements 244, 254.

Components that are in correspondence with components of the firstdisclosed embodiment described with reference to FIG. 2 perform the sameor similar functions as in the first disclosed embodiment. Thus, theywill not be described again in detail.

Referring to FIG. 3, a printed circuit board is presented in which onlythe optical waveguide 230 is formed on the flexible portion, without theelectrical wiring layer. In devices such as cell phones, both theoptical waveguide 132 and the electrical wiring layer 134 may be needed,as in printed circuit board 100 of the first disclosed embodiment,because both electrical power and analog signals may be transmitted fromthe main board to the display board. In fields requiring thetransmission only of high-speed digital signals, however, the desiredfunctions may be performed only with the optical waveguide 230, with theelectrical wiring layer removed, as presented in this embodiment.

FIG. 4 is a cross-sectional view illustrating a printed circuit board300 according to a third disclosed embodiment of the invention. In FIG.4 are illustrated a first board 210, a second board 220, vias 212, 222,ledges 218, 228, a first outer board 240, a second outer board 250,grooves 242, 252, photoelectric conversion elements 244, 254, a flexibleboard part 330, an optical waveguide 332, pads 232, rewiring lands 234,and electrical wiring layers 334 a, 334 b.

In contrast to the printed circuit boards according to the first andsecond disclosed embodiments presented in FIGS. 2 and 3, a printedcircuit board according to the third disclosed embodiment presented inFIG. 4 may have multiple electrical wiring layers 334 a, 334 b. Othercomponents that are in correspondence with components of the embodimentsdescribed above have the same or similar functions, and thus will not bedescribed again in detail.

Referring to FIG. 4, a printed circuit board 300 is presented that hasone optical waveguide 332 and multiple electrical wiring layers 334 a,334 b. The case may be contemplated where an existing printed circuitboard composed with a plurality of electrical wiring layers may havesome of the layers replaced with optical waveguides 332 to perform thedesired functions.

Furthermore, a printed circuit board 400 may be presented which has aplurality of optical waveguides 432 a, 432 b, as illustrated in FIG. 5.

In a printed circuit board 100, 200, 300, 400 according to an embodimentof the claimed invention described above, a structure may be presented,in which the photoelectric conversion elements 114, 124, 244, 254 areinstalled directly on the optical waveguide, which may minimize opticalloss.

With reference to the first disclosed embodiment of the invention asrepresented in FIG. 2, pads 136 may be formed on the optical waveguide132 for the installing of the photoelectric conversion elements 114,124, where the pads 136 may be made of copper or a correspondingconductive material. The pads 136 formed in this manner on the opticalwaveguide 132 and the photoelectric conversion elements 114, 124 may beplaced in contact by wire bonding or in the form of flip chips.

The patterns 137 extending from the pads 136 may be electricallyconnected with other layers at the rewiring lands 138 by way of the vias116, 126, etc. When the photoelectric conversion elements are formed inmultiples, the pads 136, patterns 137, and rewiring lands, etc., may beformed correspondingly, as illustrated in FIG. 6A and FIG. 6B.

In addition, as illustrated in FIG. 7A and FIG. 7B, the pads 136,patterns 137, and rewiring lands 138, etc. may be formed buried in theoptical waveguide (see FIG. 7A) or may be formed on the surface (seeFIG. 7B). When these are buried in the optical waveguide, a method maybe used, for example, of transcribing the patterns after separatepatterning work, and when they are formed on the surface, a method maybe used, for example, of performing etching after stacking a metal layeron the optical waveguide.

Next, a method of manufacturing a printed circuit board according toanother aspect of the claimed invention will be described, withreference to FIGS. 8, 9A, 9B, 9C and 9D.

FIG. 8 is a flowchart illustrating a method of manufacturing a printedcircuit board according to an embodiment of the invention, and FIG. 9A,FIG. 9B, FIG. 9C and FIG. 9D are flow diagrams illustrating a method ofmanufacturing a printed circuit board according to an embodiment of theinvention. In FIGS. 9A to 9D are illustrated first board part 110composed of a first board 110 a and a first outer board 110 b, a secondboard part 120 composed of a second board 120 a and a second outer board120 b, grooves 112, 122, photoelectric conversion elements 114, 124,vias 116, 126, ledges 118, 128, a flexible board part 130, an opticalwaveguide 132, an electrical wiring layer 134, pads 136, patterns 137,and rewiring lands 138.

First, the first board and the second board may be prepared such thatthey are separated from each other (s10). The first board 110 a and thesecond board 120 a may each be coupled to either end of the flexibleoptical waveguide 132, to allow the exchange of optical signals. Aflexible electrical wiring layer 134 may also be formed in the firstboard 110 a and second board 120 a, for exchanging electrical signals,or may be omitted in cases where an electrical wiring layer 134 is notrequired, such as when transmitting only high-speed digital data.

Next, ledges 118, 128 may be formed on the first board 110 a and secondboard 120 a on which either end of the flexible optical waveguide 132can be mounted (s20), and the flexible optical waveguide 132 may bestacked on the first board 110 a and second board 120 a such that theflexible optical waveguide 132 is mounted onto the ledges 118, 128(s30).

In other words, the method may be used of fabricating the opticalwaveguide 132 separately and inserting the optical waveguide 132 duringthe lay-up process in manufacturing the printed circuit board. For this,the first board 110 a and second board 120 a may be processed to formledges 118, 128, and the optical waveguide 132 may be stacked such thatthe optical waveguide 132 is inserted into the ledges 118, 128, afterwhich thermal compression may be performed under a high temperature andhigh pressure environment.

Afterwards, the first outer board 110 b and second outer board 120 b mayeach be stacked respectively on the first board 110 a and second board120 a (s40). Both ends of the optical waveguide 132 may then be coveredby the first outer board 110 b and second outer board 120 b, whereby theoptical waveguide 132 may be coupled with each of the first board 110 aand second board 120 a.

In the first outer board 110 b, a groove 112 may be formed to installthe photoelectric conversion element 114. By forming the groove 112 andinstalling the photoelectric conversion element 114 in the groove 112,the overall thickness of the printed circuit board may be reduced. Thisgroove 112 may be processed after the first outer board 110 b isstacked, or may be processed before the stacking so that the first outerboard 110 b may be stacked with the groove 112 already formed. Ofcourse, a groove 122 may be formed in the second outer board 120 b, justas for the first outer board 110 b, in which to install a photoelectricconversion element 124.

Also, in order that the photoelectric conversion element 114 maydirectly contact the optical waveguide 132, the groove 112 formed in thefirst outer board 110 b may be formed to a depth that allows a portionof the optical waveguide 132 to be exposed. In other words, the groove112 may be formed to penetrate the first outer board 110 b.

In a predetermined position of the optical waveguide 132 exposed by sucha groove 112, a pad 136 may be formed in direct contact with thephotoelectric conversion element 114. Thus, the photoelectric conversionelement 114 may directly contact the optical waveguide 132.

Moreover, the pads 136 may be formed buried in the optical waveguide132, to reduce the overall thickness of the printed circuit board andminimize optical loss. These pads 136 that have a buried form may beformed using a method of performing patterning work on a separatecarrier (not shown) and then transferring the patterning.

Rewiring lands 138 and patterns 137 electrically connected with the pads136 may be formed on the optical waveguide 132, and by having therewiring lands 138 be connected with the vias 116, 126, optical signalstransmitted through the optical waveguide 132 and electrical signalsconverted from the optical signals may be transmitted throughout theentire printed circuit board.

Similar to the case of the pads 136, these rewiring lands 138 andpatterns 137 may also have the form of being buried in the opticalwaveguide 132, and may also be formed using a method of performingpatterning work on a separate carrier (not shown) and then transferringthe patterning.

As set forth above, certain aspects of the invention can provide greaterbendability and reliability, by having the optical waveguide andelectrical wiring layer separated with a gap in-between at the flexibleportion of the board, and the optical waveguide can be manufactured withgreater precision, by having the optical waveguide manufacturedseparately and then inserted during the manufacturing process of theboard.

In addition, optical loss can be minimized by installing thephotoelectric conversion elements to be closely adjoining the opticalwaveguide, and the need can be eliminated for considerations on theplating characteristics with respect to the material forming the opticalwaveguide 132 or hole processing characteristics, by allowing rewiringthrough the electrical connections between the rewiring lands and vias.

While the spirit of the invention has been described in detail withreference to particular embodiments, the embodiments are forillustrative purposes only and do not limit the invention. It is to beappreciated that those skilled in the art can change or modify theembodiments without departing from the scope and spirit of theinvention.

1. A method of manufacturing a printed circuit board having a flexibleoptical waveguide to transmit optical signals, the method comprising:preparing a first board and a second board, the first board and thesecond board disposed with a gap in-between; forming a ledge on each ofthe first board and the second board such that either end of theflexible optical waveguide is mounted on each of the ledges; stackingthe flexible optical waveguide on the first board and the second boardsuch that the flexible optical waveguide is mounted by way of theledges; and stacking a first outer board and a second outer boardrespectively on the first board and the second board such that eitherend of the flexible optical waveguide is covered.
 2. The method of claim1, wherein a groove is formed adjacent to the flexible optical waveguidein the first outer board, the groove configured to have the opticalwaveguide installed therein.
 3. The method of claim 2, wherein a pad isformed adjacent to the groove on a predetermined position of theflexible optical waveguide, the pad configured to have the opticalwaveguide mounted thereon.
 4. The method of claim 3, wherein theflexible optical waveguide comprises a core through which opticalsignals propagate, and a cladding configured to cover the core, and thepad is formed by: forming a conductive pattern on a carrier, theconductive pattern corresponding with the pad; and pressing the claddingand the carrier such that the conductive pattern is transcribed onto thecladding.
 5. The method of claim 3, wherein a rewiring land is formed onthe flexible optical waveguide, the rewiring land electrically connectedwith the pad.
 6. The method of claim 5, wherein the flexible opticalwaveguide comprises a core through which optical signals propagate, anda cladding configured to cover the core, and the rewiring land is formedby: forming a conductive pattern on a carrier, the conductive patterncorresponding with the rewiring land; and pressing the cladding and thecarrier such that the conductive pattern is transcribed onto thecladding.